Pore-Pressure Response to Sudden Fault Slip for Three Typical Faulting Regimes

Abstract

The hydrological effects of earthquakes are determined by the style of fault displacement, rather than simply by the magnitude of the earthquake. In the past, many researchers used the analytical solution of Okada (1992) to estimate the porepressure field, which is derived through the stress field by Skempton's B coefficient, after the stress field is calculated from a given forced fault slip in Okada's method (Okada, 1992). This approach is a one-way coupling approach, as fluid has no effect on rock behavior, and Skempton's B coefficient must be given separately to know the pore-pressure field. We create a fault-slip model in conjunction with a poroelastic model and present a new approach in which fault movement is a consequence of reduced friction occurring in a saturated porous medium. This model represents a numerical parallel to the traditional Okada's approach, but with two advantages:(1) it is well suited for more complex geometries and heterogeneous formations for which analytical methods fail; (2) it is fully coupled so that fluid effects are also taken into account. This model shows that all three different faulting regimes exhibit completely different pore-pressure change distributions in 3D space. The transient pore-pressure change after a strike-slip faulting event is axis symmetrical with respect to the imaginary vertical line passing through the epicenter and hypocenter, with increased and decreased areas evenly distributed in a juxtaposed pattern. The transient pore-pressure changes associated with normal and thrust faulting all display a circular pattern on the model surface, with the largest pore-pressure increase occurring at the epicenter for normal faulting and the largest decrease for thrust faulting. Many observed field phenomena have been explained in surprising detail by this model.

Spatiotemporal Evolution of Pore Pressure Changes and Coulomb Failure Stress in a Poroelastic Medium for Different Faulting Regimes

“…In this study we have modeled the spatiotemporal evolutions of ΔCFS generated by three typical faulting earthquakes in porous medium. The co-seismic pore pressure change patterns are similar to the results in previous study (Zhou & Burbey, 2014). The co-seismic ΔCFS patterns calculated by our FEM models are similar to the patterns computed by Okada's analytical solution in general, but in the near-fault area where the co-seismic pore pressure is large, the co-seismic ΔCFS is clearly different from that obtained using analytical solution.…”

Spatially and temporally systematic hydrologic changes within large geoengineered landslides, Cromwell Gorge, New Zealand, induced by multiple regional earthquakes

“…On this basis, some mechanisms commonly proposed to explain hydrological response to earthquakes can quickly be discounted in this case. For example, the local variations in polarity cannot be explained by volumetric strain associated with distal fault slip [e.g., Ge and Stover , ; Jónsson et al ., ; Zhou and Burbey , ]. With a lack of earthquake‐related changes in extensometer and inclinometer data, or any detected motion requiring mitigation after intermediate and far‐field earthquakes, the systematic hydrologic changes seem equally unlikely to be the result of volumetric strains associated with otherwise undetected movement of the now heavily engineered landslides.…”

Potential of porosity waves for methane transport in the Eugene Island field of the Gulf of Mexico basin

“…They predicted maximum hydraulic head increases of about 130 m near the fault, which equates to pore fluid pressure increases of about 1.3 MPa. Zhou and Burbey (2014) modeled pore fluid pressure responses to sudden slip on normal, strike-slip, and reverse faults as a result of sudden fault plane slip at depths of about 5 km. They predicted maximum pore pressure increases near the fault on the order of 1's of MPa for decimeter-scale fault plane slip, and 10's of MPa for meter-scale fault plane slip.…”